Integrated circuits have utilized bipolar junction transistors for many years, taking advantage of their high gain characteristics to satisfy high performance and high current drive needs. In particular, as is well known in the art, bipolar transistors are especially well-suited for high frequency applications, such as now used in wireless communications.
Silicon-on-insulator (SOI) technology is also well-known in the art as providing important advantages in high-frequency electronic devices. As is fundamental in SOI technology, active devices such as transistors are formed in single-crystal silicon layers formed over an insulator layer, such as a layer of silicon dioxide commonly referred to as buried oxide (BOX). The buried oxide layer isolates the active devices from the underlying substrate, effectively eliminating parasitic nonlinear junction capacitances to the substrate and reducing collector-to-substrate capacitances. To the extent that high frequency performance of bulk transistors was limited by substrate capacitance, SOI technology provides significant improvement.
Record fTpeak*BVCEO product has been achieved for both NPN and PNP. This was possible due to re-surf effect from the substrate through buried oxide on low-doped collector region.
However, high cost of SOI substrates prohibit mass product development using this technology. In addition, a split voltage source is required to implement re-surf effect in PNP (for a grounded substrate). It has also been observed that significant self-heating occurs at currents above fTpeak and large VCE.
A conventional SOI bipolar transistor is designed to be a high performance device. However, a high performance transistor is somewhat limited by its construction, from a standpoint of both breakdown voltage and performance. As is fundamental in the art, the collector emitter breakdown voltage (BVCEO) depends upon the thickness of collector region and upon the doping concentration of the collector region. Lighter doping of the collector region and a thicker collector region would increase this breakdown voltage.
In real circuits, the emitter and bases complementary SiGe bipolar junction transistor (BJTs) are biased around the highest potential Vcc (relative to grounded substrate) while the collectors are switched between Vcc and 0. High B-C bias corresponds to zero potential at collector.
What is needed is a method of increasing PNP BV without decreasing collector doping concentration or increasing collector region thickness of the PNP while including a high voltage NPN on the same bulk processed circuit/substrate.